Maintain your Windows Updates
Keep your computer(s) behind a NAT router. Most cable ISPs only give you a modem, so your computer gets a public IP address. This is riskier. Most DSL ISPs now are shipping modems which are actually little combo modem/routers, so you're usually protected behind NAT already. NAT, besides other gateway functions, gives you basic hardware firewall protection from inbound unknown traffic (basically..hides your computer). Software firewalls can become corrupted, and cause other issues on your computer (most notably...zone alarm...ugh), thus they're not a good primary line of defense. A NAT router is always there protecting you from strange inbound..which is what counts.
Never leave your Administrator password blank. Lots of malware can install assuming this.
Use a quality antivirus that is frequently updated.
I prefer Esets NOD32 for paid, Kaspersky is also very good. I've disliked Symantec/Norton for many years due to "bloat"..but their most recent version..2009, is actually VERY light now.
For freebie antivirus, AntiVir is hands down tops in detection and also lightest of the freebies.
www.av-comparatives.org is a great place to read up on "real world, unbiased" comparisons of various antivirus programs.
Ad/Spyware is getting bad, especially the "rogue" fake malware such as XPAntivirus2009, Antivirus360, WinFixer, etc. Good to have an additional ad/malware prevention program. Spybot Search and Destroy (installed without the teatimer option), and SpyWareBlaster are 2x good programs that do not slow down your system at all. Keep them both updated frequently, and each time you update Spybot..go and run the "immunize" function again.
For cleaning infections of the above pesky rogues....based on the Vundu/ZLob trojans, using MalwareBytes, SuperAntispyware, Spybot, Adaware, and following up with Microsofts own Malicious Software Removal Tool works well.
Firefox web browser with the Adblock Plus plugin...keeps your web surfing a bit less annoying with ad banners, and it's less prone to exploits compared to IE.
RAM RAM RAM..cheapest upgrade you can do for your computer. XP is OK with 512, better with a gig. 2 gigs gets to be the law of diminishing returns for average computer users. If you're running heavy programs like graphics editing or gaming....go for 4 gigs. Yeah 32 bit Windows will only "show" you somewhere from 3.0 or 3.2 or 3.6 gigs (depending on your hardware)...but with memory, you get better performance from matched pairs...so for 4 gigs, stick with matching 2x 2 gig pairs or 4x 1 gig pairs. This way you benefit from the "DDR" synchronous pairing..higher speeds across the bus.
For Vista users, starting with 2 gigs of RAM is a good place, 4 gigs for heavier users. (or more if you're running 64 bit).
Running wireless at home? Make sure it's secured. Unsecured can result in the kid next door leeching from your connection...slowing you down. Kiddies next door are also more likely be downloading warez and pirated stuff..which comes bundled with trojans and other malware. If he's using your wireless connection..he's on your network. Lots of that malware can spread across networks. So if his PC is infected, and he's on your open wireless...he's actually on your network..with your PC..and your PC can get infected.
Shopping for laptops? Double the RAM you'd normally do for a desktop PC. Also, make sure you get at least a 5,400rpm hard drive, better yet..7,200rpm hard drive. Many more "entry level" basic laptops come with only a 4,200rpm hard drive..the biggest reason laptops seem much slower than their equivalent CPU desktop counterpart. Getting extra RAM and upgrading that hard drive speed brings back near desktop performance.
Yep, I could sure use cooksie around for my wire / rats nests. I start them out all neat but over time and adding this and that they always become a mess. Maybe someone is knotting them all together when I'm not looking. 
